Far infrared CO and H2O emission in intermediate-mass protostars
Abstract
Intermediate-mass young stellar objects (YSOs) provide a link to understand how feedback from shocks and UV radiation scales from low to high-mass star forming regions. Aims: Our aim is to analyze excitation of CO and H2O in deeply-embedded intermediate-mass YSOs and compare with low-mass and high-mass YSOs. Methods: Herschel/PACS spectral maps are analyzed for 6 YSOs with bolometric luminosities of Lbol102 - 103 L. The maps cover spatial scales of 104 AU in several CO and H2O lines located in the 55-210 μm range. Results: Rotational diagrams of CO show two temperature components at Trot320 K and Trot700-800 K, comparable to low- and high-mass protostars probed at similar spatial scales. The diagrams for H2O show a single component at Trot130 K, as seen in low-mass protostars, and about 100 K lower than in high-mass protostars. Since the uncertainties in Trot are of the same order as the difference between the intermediate and high-mass protostars, we cannot conclude whether the change in rotational temperature occurs at a specific luminosity, or whether the change is more gradual from low- to high-mass YSOs. Conclusions: Molecular excitation in intermediate-mass protostars is comparable to the central 103 AU of low-mass protostars and consistent within the uncertainties with the high-mass protostars probed at 3·103 AU scales, suggesting similar shock conditions in all those sources.